8.3 ISC 250 power concerns

[Bjorkinman]

Hey all, I’m new to the site and looking at a bus for sale. It’s a 2000 Thomas with the 8.3 isc 250 paired with an MD3060, which is the combo I’ve been looking for for quite some time. I know this is the CAPS system so a fass or air dog lift pump would be on short order if I buy it. My question is whether or not this 250 version would be enough power to get around comfortably? And if needed can I increase the power with a banks system given the cooling capacity? It’s 40ft and I plan to tow a jeep behind.
I already test drove it and it died on us while driving.. im fairly pretty certain it was a fueling issue because the bus was making intermittent power and when the power dropped the check engine light would come on. If I elect to buy this bus, I would first send off an oil sample to see what comes up in the report. It ran great at idle and when the bus did seem to make power it was fine. It was just those few times when the power lagged and the checked engine light flashed. Thanks all in advance for your input.

[fo4imtippin]

I think you would be fairly happy with the 250hp. Those rear engines don't have air being rammed down the radiator and intercooler, so its tougher than a front engine to keep cool. It can be done, and probably with no worry up to 300hp, but beyond that, you are going to be teetering with reliability and longevity. Not sure about banks on the ISC, but i would look at having a CAL flashed by cummins insite. They ran that motor in rear engine motorhomes from the factory at over 300hp.



I have an ISB with a 225hp tune. Originally i was all about turning it up, but the longer i have it, the less concerns with power i have, its easy to drive as is, so i don't want anything more to worry about if i turn it up. The good news on the ISC is that the torque is even bigger to push you up hills faster than the little ISB.

[Bjorkinman]

Thanks for that, gives me more clarity about what I’m looking at. I’m like you, I don’t mind running a little slower to be age with it, but knowing that I’m towing and bound for the Rockies is what had me wondering.

[TJones]

Originally Posted by Bjorkinman

Hey all, I’m new to the site and looking at a bus for sale. It’s a 2000 Thomas with the 8.3 isc 250 paired with an MD3060, which is the combo I’ve been looking for for quite some time. I know this is the CAPS system so a fass or air dog lift pump would be on short order if I buy it. My question is whether or not this 250 version would be enough power to get around comfortably? And if needed can I increase the power with a banks system given the cooling capacity? It’s 40ft and I plan to tow a jeep behind.
I already test drove it and it died on us while driving.. im fairly pretty certain it was a fueling issue because the bus was making intermittent power and when the power dropped the check engine light would come on. If I elect to buy this bus, I would first send off an oil sample to see what comes up in the report. It ran great at idle and when the bus did seem to make power it was fine. It was just those few times when the power lagged and the checked engine light flashed. Thanks all in advance for your input.

If the bus seems like it is having fuel issues you may want the seller to replace the fuel filters and see if the stalling problem goes away before purchasing the bus. It could also be that the CAPs pump is going bad. You may want to check on the cost of having a new pump installed before you commit to this bus.

Ted

[Bjorkinman]

Originally Posted by TJones

If the bus seems like it is having fuel issues you may want the seller to replace the fuel filters and see if the stalling problem goes away before purchasing the bus. It could also be that the CAPs pump is going bad. You may want to check on the cost of having a new pump installed before you commit to this bus.

Ted

Yes I think I’ll do that, I know the CAPS pump on those things is pretty costly, and from what I’ve seen I also think it needs to be timed as well. Looking over at irv2 a lot of RVers have had issues with this and it ended up being that the 3 bolts on the stock lift pump were loose and allowing fuel/air to leak by. This issue arose from the introduction of ULSD in 2006 degrading the gasket.

[Bjorkinman]

By the way, I think my family and I are looking at Rapid City as a possible new home after we settle down from traveling.

[LargeMargeInBaja]

Our 1996 rig has a Cummins 8.3-liter/litre 250hp mechanical through an Allison 3060.
.
Weight across the scale -- 14,000#.
We did a circuit of South America and over to Alaska towing a 1991.5 Dodge Cummins 4x4 weighing right at 8,000#.
.
We putter along in the 'slow' lane at 52mph... although the rig and we prefer rustic rural two-lanes.
.
Based on two decades with this combination, we are coming to the conclusion it is barely adequate on mountain freeways.
.
Fussing with the pump would always be an option for greater performance, but we are up against the limits of the rest of the train -- trans, U-joints, brakes, etcetera.
.
More power creates the potential for breaks, and we tend toward conservative.
That 'getting home in one piece' philosophy.

[cadillackid]

alot has to do with gearing.. with an MD3060 you may be geared lower on the rear which gives you help in the torque department when it comes to accelerating.. the 3060 will have a 0.75 overdrive... so look at rear gears which helps you determine your top and crusing speeds as well as what kind of torque you'll have in the hills.. if that bus has a 4.44 gear it will have a really high top speed but will be paltry climbing or accelerating.. if it has a 5.13 or 5.39 your top speed is lower (but helped by the overdrive) and you'll have a better time of it climbing and accelerating in your lower gears...

[TJones]

Originally Posted by Bjorkinman

By the way, I think my family and I are looking at Rapid City as a possible new home after we settle down from traveling.

It's a nice place to live but don't tell anyone else. It's starting to get crowded.

Ted

[Bjorkinman]

We were there last year on our annual road trip, compared to Atlanta anything feels small! Stayed two days and didn’t want to leave.

[Bjorkinman]

Thanks Cadillac. I’m not sure as of yet what the gearing is. This is helpful though, I doubt they’ve had 6th gear unlocked which I may try to get done. I’ve seen some posts here related to doing that that really looked helpful.

[LargeMargeInBaja]

Originally Posted by cadillackid

alot has to do with gearing.. with an MD3060 you may be geared lower on the rear...if that bus has a 4.44 gear it will have a really high top speed but will be paltry climbing or accelerating.. if it has a 5.13 or 5.39 your top speed is lower...

.
Good point.
.
Our axle ratio is 6:88 according to the differential tag.
.
This's fine with us, because we often creep rough logger tracks.
During the descent, I keep the trans in first gear to reduce my braking.
.
An aside:
If we were serious about mountain braking, we could swap our 3060 for a similar trans with the retarder.
.
We delivered a firetruck with a 4060 (3060's honkier sibling) and three-position retarder with the thumb-operated switch on the steering-wheel.
Releasing the throttle with the retarder engaged -- at the lowest position 'ONE' -- nearly threw us onto the dash.
Not quite, but the non-brake slowing was impressive.
.
We speculated the upper positions could toss us through the windshield.
.
Unfortunately, Allison tells me 3060 internal circuits are different, so the retarder is not a DIY add-on.
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https://youtu.be/Nx9Drp6oymU

[cadillackid]

Originally Posted by LargeMargeInBaja

.
Good point.
.
Our axle ratio is 6:88 according to the differential tag.
.
This's fine with us, because we often creep rough logger tracks.
During the descent, I keep the trans in first gear to reduce my braking.
.
An aside:
If we were serious about mountain braking, we could swap our 3060 for a similar trans with the retarder.
.
We delivered a firetruck with a 4060 (3060's honkier sibling) and three-position retarder with the thumb-operated switch on the steering-wheel.
Releasing the throttle with the retarder engaged -- at the lowest position 'ONE' -- nearly threw us onto the dash.
Not quite, but the non-brake slowing was impressive.
.
We speculated the upper positions could toss us through the windshield.
.
Unfortunately, Allison tells me 3060 internal circuits are different, so the retarder is not a DIY add-on.
.
https://youtu.be/Nx9Drp6oymU

the 3060s "bus-specific" vocation cousin was made with a retarder.. the B300R. when you look at them you think they are the same but the R at the end means retarder.. the B series were specifically designed for busses.. Im not sure what all is different...



you could however add a Telma retarder... we have seen busses come through this forum that have them, though definitely not super common.. with your 6.xx gear (my classic superior gas bus had that gear in it). you probably have decent engine compression braking

[rossvtaylor]

And to add on to Christopher's notes, we've had 3 Gillig transit buses with B400R transmissions and the retarder function on those was really impressive.

I enjoy your posts and adventures...even if I don't comment or say so every time! Thanks for sharing.

[Bjorkinman]

I’ve seen the banks power pack for the isc 350’s comes with what looks to be a retarder. Along with a new turbo wastegate and tuner like device. I don’t know if they have that system available for the 250, but again the concern that a pusher would have insufficient cooling capability. Seems like my best bet would just be to get 6th unlocked and make sure the gearing is set up a little taller. Thanks everyone for your inputs.
Man a 6.88 - I didn’t even know they put those in, but I guess I’m not surprised.

[cadillackid]

Originally Posted by Bjorkinman

I’ve seen the banks power pack for the isc 350’s comes with what looks to be a retarder. Along with a new turbo wastegate and tuner like device. I don’t know if they have that system available for the 250, but again the concern that a pusher would have insufficient cooling capability. Seems like my best bet would just be to get 6th unlocked and make sure the gearing is set up a little taller. Thanks everyone for your inputs.
Man a 6.88 - I didn’t even know they put those in, but I guess I’m not surprised.

school busses in north carolina came with 7.17s at one time to prevent them from going over 45 MPH mechanically (so mechanics couldnt remove the governer)...


my 1978 Superior had 6.xx gearing as it lived in the hills of a small town in eastern oregon so they wanted it to climb hills well but being it never used the freeways (and in 1978 the top speed limit in USA was 55).. they set it up low geared...

[Jolly Roger bus 223]

my 86 nc bus as well as all of the mechanical nc buses in my area of the era are governed and geared with 6.50 rear and 175 hp to run 49mph on flat land.
i have hit 51 once or twice downhill but it holds itself back.
when i get my other projects out of the way it will be getting a powertrain upgrade.
my wifes chevy cutaway shortie with the 6.0 gas had no problems running the interstate at 80 and felt like it had more in it but i was already pushing it running without tags or insurance to bring it home.